The invention relates to a "sheet"-type electron multiplier dynode, i.e., the dynode comprises two half-dynodes which are in the form of sheets in which apertures are formed which are arranged according to a pattern having a specific configuration. The invention also relates to an electron multiplier and a photomultiplier tube comprising such multiplier dynodes.
The invention can be very advantageously used in the field of photomultiplier tubes.
The use of dynodes and "sheet"-type multipliers in photomultipliers tubes is known from, for example, French Patent Specification No. 2 549 288. This specification describes an electron multiplier dynode which comprises two parallel arranged half-dynodes to which an equal potential is applied and which are manufactured by using metal sheets in which apertures are formed which are regularly arranged according to a recurring pattern having one and the same basic configuration. In a multiplier comprising a number of such dynodes, the first half-dynode serves as the electron-extracting electrode, which extracts the electrons emitted by the preceding dynode, and the second half-dynode is the electron-emitting electrode. For this reason, the apertures in the emitting half-dynode are substantially funnel-shaped so that the walls of the apertures, which are covered by secondary-emission material, form the useful electron multiplication zones. The secondary electrons thus formed, which are attracted by the next extracting electrode, pass through the emitting half-dynode via the aperture from which they originate. Photomultiplier tubes in which "sheet"-type multipliers are used have many advantages. While occupying little space, the photomultiplier tubes have a large collection surface, which renders them very advantageous when the electrons are incident in the form of a wide beam, as in the case of proximity focussing or in the case of application in combination with a large focussing first dynode. In addition, the possibility of partitioning the multiplier enables the formation of a certain number of secondary photomultiplier tubes in one and the same tube, which has been advantageously used in nuclear physics, for example, for exactly localizing detected particles.
However, the electron multiplier dynodes known from the present state of the art have the disadvantage that the funnel-shaped apertures which are necessary for the multiplying the electrons require a relatively costly manufacturing process comprising chemical attack and the use of masks. Moreover, it is to be noted, that with a view to increasing the multiplier surface, the output opening of the apertures is relatively small, which complicates the correct positioning of the metal sheets relative to one another inside one and the same electron multiplier.